“Jesus, Paul & Peter all used Scripture as authoritative.”
Yes, they did. Hebrew Scripture, as they were all Jews - and Septuagint Hebrew Scripture at that, as it was the only one around at that point.
The New Testament Canon was not finalized until the 4th Century...by (GASP!!!) Orthodox Bishops...out of the (GASP!!!) tradition of the Church. The first known evidence of the New Testament books in the form which they are known today was in an Easter letter by St. Athanasius in 367, between the first (Nicea) and second (Constantinople) Ecumenical Councils.
Anything else is, as Kolo would put it, ahistorical nonsense.
The Canon recognized what the Church was already using...notice 2 Peter mentions the writings of Paul as Scripture, while Paul quotes Luke as Scripture.
Nothing against the Old Testament, but the church did NOT wait 400 years before using the New as Scripture. Most of the 27 book canon was accepted without question, but about 5 books were in doubt - and several other possible candidates were considered (and thus, being used by some congregations at that time).